The term "water-based functional fluid" is used herein to refer to water-based lubricants, hydraulic fluids, cutting fluids and the like. The use of water-based functional fluids is not a new concept. However, in recent times, the increasing cost and scarcity of petroleum has made it increasingly desirable to replace oil-based fluids with water-based fluids wherever possible. Other benefits can also flow from such replacements such as decreased fire hazard and environmental pollution problems. In many cases, however, it is not feasible to make such replacements because the water-based fluids cannot be modified in their properties so as to perform to the same high degree as their oil-based counterparts. For example, it has been often difficult, if not impossible to replace certain oil-based hydraulic fluids with water-based fluids even though the desirability of doing so is evident.
A considerable amount of interest has been expressed in thickening water-based functional fluids to overcome performance limitations associated with unthickened fluids. These limitations involve, for example, the following general functions: improved fine feed control of valving for precise clamping and positioning operations; and improved pump efficiency by reducing internal leakage (particularly in vane pumps).
Various thickening agents for use in water-based functional fluids have been proposed. Examples of these thickening agents include the polysaccharides and various synthetic thickening polymers. Among the polysaccharides are the natural gums such as gum agar, gum Arabic, dextran, cellulose ethers and esters such as hydroxyethyl cellulose and the sodium salt of carboxymethyl cellulose. Other thickeners include synthetic polymers such as polyacrylates, polyacrylamides, hydrolyzed vinyl esters, polyvinyl pyrrolidones and homo- or copolymers as well as soluble salts of styrene, maleic anhydride copolymers. See, for example U.S. Pat. Nos. 2,455,961; 2,944,976; 2,956,951; 3,005,776; and 4,257,902.
The use of water-based functional fluids containing anti-wear agents is also not new. Examples of such anti-wear agents include dibutyl ammonium laurate. See, for example, U.S. Pat. Nos. 2,944,976 and 4,257,902.
There is a continuing need for organic thickening agents that are suitable for use in water-based functional fluids. It would be advantageous if such a thickening agent could be provided that also imparted other advantageous properties, such as anti-wearing characteristics, to such functional fluids.